Space weather "driver" discovered

The Solar and Heliospheric Observatory captured this ultraviolet image of a large solar prominence stretching away from the sun. Prominences are huge clouds of relatively cool, dense plasma suspended in the solar corona. Magnetic fields build up tremendous forces to propel particles in a prominence away from the sun's surface. For scale, this prominence extends 30 Earth diameters away from the sun.

SOHO / NASA / ESA

December 12, 2006Scientists at the American Geophysical Union (AGU) meeting in San Francisco announced on Monday they have found the "driver" that governs space weather near Earth. New findings show that aurorae and other effects of space weather are governed by the rate at which magnetic fields from the Sun and Earth connect, or merge. The effects do not result from the solar wind's electrical field, as solar physicists previously believed. The merging of the magnetic fields takes place at about 40,000 miles above Earth's surface, and is a "fundamental" part of the circulation of particles between Earth and the Sun, say the scientists.

The researchers, led by Patrick Newell of the Johns Hopkins Applied Physics Lab in Baltimore, have created a formula that describes the rate of merging of the magnetic field lines and predicts 10 different types of near-Earth space weather activity, such as aurorae and various magnetic disturbances.

"Having this formula is a big step forward for understanding how the Sun and Earth interact," says Newall. That understanding, he contends, could help predict the space weather that affects communications, navigation, and the health of humans in space.

Deciphering the interaction between Earth and the Sun is an extremely complex challenge, tantamount to analyzing trillions of particles and understanding why they interact the way they do. The energetic particles filling the space between Earth and our star were produced by the Sun's atmosphere. High temperatures, typically a few million degrees, accelerate these particles into a stream, called the solar wind, to a velocity of about a million miles an hour. Space weather researchers have long thought near-Earth space weather phenomena could most easily be predicted by the solar wind's electrical field. But Newell and his colleagues now become the first to put this idea to a rigorous test.

The team unraveled NASA satellite observations of global auroral activity, NOAA satellite observations of the stretching of Earth's magnetic field lines on Earth's nighttime side, and U.S. Air Force satellite observations of the how solar wind particles entered Earth's upper atmosphere. They questioned whether the electrical field activity was really the best predictor, or if each phenomenon requires its own formula, and in the end were delighted and surprised to find their single formula could provide the best clues to how 10 aspects of space weather behave.